Milestone dateexpected and release datereleased wrong type in db

The Milestone.dateexpected should be changed into a date column, since the class defines the field as a DateCol.

Currently, the Milestone storm objects set dateexpected to a datetime.datetime object when retrieving a Milestone from the DB, but it sets it to a datetime.date object, when changing the date in code. This causes problems when sorting a list of milestones, since datetime.datetime and datetime.date objects cannot be compared.